Moonrise & Aurora

Moonrise & Aurora

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How is it that the FOV can be greater for the smaller resolutions in their camera, which has no zoom? I would expect a greater FOV when more of the sensor is used.

From: http://gopro.com/cameras/hd-helmet-hero-camera/

  • Angle of View: 170º ultra wide angle in WVGA, 720p, or 960p mode
  • Angle of View: 127º wide angle in 1080p mode

Can someone explain that in technical terms?

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I would guess that the sensor looks like this: A_A_ABABABABA_A_A; in each row, there are 1280 pixels of type A and and additional 960 pixels of type B in the middle part. If you crop the middle part and take both A and B pixels, you will have the horizontal resolution of 1920 (and narrow field of view). If you take all A pixels, you will have the horizontal resolution of 1280 (and wide field of view). – Jukka Suomela Feb 25 '11 at 14:19
@Jukka I think you might be right, post an answer so you can get some credit – mandrake Feb 28 '11 at 7:05
@Jukka you may be right but it seems like a lot of effort to go to in order to provide slightly higher def in the centre of the frame and I doubt GoPro manufacture sensors so they'd have to commission a custom design which would cost a lot more than buying a stock sensor. – Matt Grum Feb 28 '11 at 18:16
Actually from the specs the camera can take 5mp stills, so it is variable subsampling rather than a A_A_ABABABABA_A_A design – Matt Grum Feb 28 '11 at 18:24
@Matt Grum - Unless that's 5mp interpolated – Fake Name Mar 2 '11 at 8:24

2 Answers

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The only thing I can think of is that the cam doesn't have the processing power to encode all the pixels in the sensor, so you can either crop the frame (which reduces the field of view) or you can use the whole sensor and subsample (skip pixels/rows like video DSLRs do), which reduces the resolution but maintains the full field of view.

edit: looking more closely at the specs, the HD hero takes 5MP stills so it must be a case of variable subsampling rates. Given this I can't see why they couldn't produce a 1080p signal by subsampling the whole sensor. I wonder if it's something to do with the lens, i.e. it's too soft in the corners for full HD.

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Yeah, that's my understanding as well. And it doesn't explain the increased field of view for lower resolutions. Only that the FOV can be the same or smaller for lower resolutions. I think Jukka might be right in his comment. – mandrake Feb 28 '11 at 7:04
up vote -1 down vote

I'm pretty sure that at lower resolutions, the image is binned 2x2 (only one pixel of each 4 pixel square is used). At the higher res mode, there aren't enough pixels to 2x2 bin, so the image is just cropped (1920x2 > total # horizontal pixels). Thus, wider FOV at lower res.

So pixel usage looks like: x_x_x_x_x_x (6 pixels, wide) vs xxxxxxxx (8 pixels, narrow)

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Pixel binning usually means the four pixels are combined at the sensor read level, not that all but one of the pixels is discarded. – mattdm Dec 1 '11 at 9:52

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